While the main body of the Utah Symphony was doing its duty at "Cosi fan tutte," the rest of the orchestra did its part to help usher in the Mozart year Saturday at Symphony Hall via a "Mostly Mozart" program - now where have we heard that term before? - with associate conductor Kirk Muspratt at the helm.

"Mostly" because for some reason it was decided to finish off the first half with Haydn's Cello Concerto in C major, the one that finally resurfaced in Prague in 1961. Soloist in this was the orchestra's principal cellist, Ryan Selberg, who despite some trouble in the runs, and occasionally the upper register, turned in a virile, mostly straightforward account.Especially praiseworthy was the continuity he brought to the writing, whether in the first movement, here firmly propelled by Muspratt, or the meditative Adagio. Seldom if ever did the line sag, least of all in the controlled high spirits of the finale.

Even without the Haydn, though, the program's original title, still to be seen on the tickets, would not have been appropriate. For instead of "The Many Faces of Mozart," what we got was pretty much the one that wears a smile.

Particularly in the piece that opened the second half, the K. 251 Divertimento in D major. Apparently composed in honor of his sister's birthday, this delightful opus finds Mozart, then in his 21st year, in a cheerfully inventive frame of mind.

And Muspratt too, as it happens, as he did not hesitate to invert the order of the last two movements, concluding the piece not with the French-style Marcia that almost certainly saw the original musicians on their way but with the Rondeau, whose good-humored vitality made for a much more satisfying conclusion.

Throughout the musicians were his willing accomplices, from the semi-galumphing opening movement, with its spicy horn contributions, to the characterful string accents of the first minuet. Best of all, perhaps, were the oboe and violin solos of the second minuet, here structured as a theme with variations, and the aforementioned Rondeau. Credit James Hall and Ralph Matson for those, respectively.

Indeed, I would not have minded had a little more of that character carried over to the performance of the Symphony No. 33 in B flat major, which after a somewhat tepid opening came together nicely, if a bit too temperately in spots. But it would be a mistake to discount the graceful thrust of the outer movements or the restraint Muspratt and his players brought to the third-movement trio.

For the fact is, apart from a tendency to expand a bit too much in the lyrical episodes (e.g., the slowish Andante of the symphony), Muspratt is clearly an accomplished Mozartean. And that was no less evident in his bracing account of the curtain raiser for the evening, the early Overture to the opera "Lucio Silla," which, although it also took its time over the slower pages, was otherwise notable for its vigor and crispness, even in the unison trills.

What I question here, however, were the pauses between sections. Admittedly, this work is more a symphony than an overture, given its Molto allegro-Andante-Molto allegro layout. But that harks back to the baroque conception of an overture, and either way I doubt they'd have stopped between them in the opera house.

Even then, they generally saved that for the arias.